The specific objective of the proposed investigation is the application of a new technique of oxygen tension measurement to the clinical determination of Po2. The ability to continuously monitor arterial Po2 would greatly enhance the clinical management of respiratory distress syndromes in both anesthesiology and neonatology. Of particular concern is the continuous monitoring of the immediate effect of pharmacological and mechanistic therapy on gas exchange. The overall goal of the proposed research is the development of a system of measurement which will allow continuous direct determination of the absolute partial pressure of oxygen (Po2) in vivo. This system will be based upon a new technique which measures the net charge transport to the indwelling sensor. This technique effectively determines the difference in charge transport that occurs during the polarization pulse and during a related time following removal of the polarization potential. There are three unique factors of this new measurement technique which provide the basis for the proposed research. First, the retention of the diffusion gradient to within less than 8 um of the cathode surface due to short duration pulsing. This allows the application of a special protective coating which will enable the control of the media parameters which affect the oxygen measurement and provide a highly compatible interface between the sensor and arterial blood. Second it is possible the construct a solid state sensor of a size which will allow insertion through an 18 gauge needle. Third, the measurement and subsequent analysis of the transient behavior of the electrochemical cell should allow the development of an in vivo calibration technique.